Dawn arrives at Vesta

Dawn Space Probe

NASA's Dawn spacecraft has returned the first close-up image after beginning its orbit around the giant asteroid Vesta. On Friday, July 15, Dawn became the first probe to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

Vesta is 330 miles (530 kilometers) in diameter and the second most massive object in the asteroid belt. Ground- and space-based telescopes have obtained images of Vesta for about two centuries, but they have not been able to see much detail on its surface. This is beginning the study of arguably the oldest extant primordial surface in the solar system. This region of space has been ignored for far too long. So far, the images received to date reveal a complex surface that seems to have preserved some of the earliest events in Vesta's history.

Vesta is thought to be the source of a large number of meteorites that fall to Earth. Vesta and its new neighbour Dawn, are currently approximately 117 million miles (188 million kilometers) away from Earth. The Dawn team will begin gathering science data in August. Observations will provide unprecedented data to help scientists understand the earliest chapter of our solar system. The data also will help pave the way for future human space missions.

The probe carries instruments to detect the mineral and elemental composition of its surface rocks. It will be looking for evidence of geological processes such as mountain building and rifting.

The Dawn science team is keen to understand how Vesta's surface has been remodelled over time by impacts and even lava flows. Dawn's remote sensing instruments will also be able to discern something of the asteroid's internal structure. The expectation is that scientists will confirm it has a metallic core. From the outside, Vesta looks like a punctured football, the result of a colossal collision sometime in its past that knocked off its south polar region.

After traveling nearly four years and 1.7 billion miles (2.8 billion kilometers), Dawn accomplished the largest propulsive acceleration of any spacecraft, with a change in velocity of more than 4.2 miles per second (6.7 kilometers per second), due to its unique ion engines. The engines expel ions to create thrust and provide higher spacecraft speeds than any other technology currently available.

Dawn will spend one year orbiting Vesta, then travel to a second destination, the dwarf planet Ceres, arriving in February 2015.